The present invention relates to law enforcement technologies and security, and more particularly to methods and systems for estimating the location of a shooter firing a supersonic projectile based on shockwave-only information.
Systems and methods are known that can determine the general direction and trajectory of supersonic projectiles, such as bullets and artillery shells, by measuring parameters associated with the shockwave generated by a projectile. One such system, described in U.S. Pat. No. 5,930,202 utilizes a distributed array of acoustic sensors to detect the arrival times, amplitudes and frequency characteristics of a projectile's shockwave and the muzzle blast from a firearm. The time of arrival (TOA) information for the shockwave can be used to determine the projectile's trajectory: azimuth, elevation, and intercept with an arbitrary plane in the system coordinate frame. With additional information from the muzzle blast, an accurate location of the origin of the projectile and a line of bearing to the origin of the projectile can be determined. When the muzzle blast is masked, shadowed, silenced or otherwise distorted, at least the bullet trajectory can be estimated from the shockwave alone.
Conventional systems typically employ an antenna with a plurality of acoustic sensors, which can be relatively closely spaced (e.g., 1 meter apart) or widely dispersed (e.g., mounted on a vehicle or carried by soldiers on a battlefield), with each sensor measuring shockwave pressure omni-directionally at its respective location. One exemplary antenna may include, for example, a total of 7 omni-directional microphones, with 6 microphones distributed over the surface of a sphere (approx. diameter 1 m) and the seventh microphone located in the center of the sphere. An arrangement with less than 7 sensors can produce objectionable lobes in the spatial sensitivity pattern of the sensor array.
Sensor positions can shift over the service life of a deployed system and/or sensor performance can degrade over time for various reasons. Occasionally, some sensors may stop operating altogether.
It would therefore be desirable to provide a system and method that compensates for changes in sensor position and sensor performance by calibrating themselves automatically or with operator assistance.